Osteoporosis diagnosing apparatus and method

ABSTRACT

The osteoporosis diagnosing apparatus of the invention radiates repeatedly an ultrasonic impulse Ai toward the bone Mb of an examinee and receives an echo Ae from the bone Mb. The received signal is converted into a digital echo signal through an A/D converter (8), and the echo level is detected by a CPU (11). The CPU (11) extracts maximum echo level from among the echo levels detected in a given period of measurement to thereby calculate a bone acoustic impedance Zb based on the extracted maximum echo level, and then calculate the bone density of the examinee based on the calculated acoustic impedance Zb. As the impedance Zb is expressed in the square root of the product of modulus of elasticity and density of a bone, decreased in both the modulus of elasticity and the density synergistically affect the impedance to remarkably decrease the same. Thus the bone acoustic impedance serves as a good index in judging the bone density

TECHNICAL FIELD

This invention relates to a reflection type ultrasonic osteoporosisdiagnosing apparatus and method which diagnoses osteoporosis byradiating ultrasonic impulses towards a certain bone (cortical bone) ofan examinee and determining echo levels from the surface of the bone;

BACKGROUND ART

With the emergence of an ageing society in recent years the bone diseasetermed osteoporosis has been becoming a problem. In this disease thecalcium is withdrawn from the bones leaving them friable and prone tofracture at the slightest shock. Physical diagnosis is performed mainlyby determining the density of bone precisely by means of diagnosticapparatus employing X-rays, typified by DXA apparatus; however, physicaldiagnosis by means of X-rays is beset by various problems such as thefact that the apparatus is large, and its use is restricted by the needto prevent damage due to radiation exposure.

Accordingly, diagnostic apparatus employing ultrasound have started tobecome popular as simple apparatus which do not cause such problems. Indiagnostic apparatus employing ultrasound the speed and attenuation ofultrasound waves propagated inside the bony tissues are measured andused to estimate the density and elastic modulus (elastic strength) ofthe bone, and if a low estimated value is obtained it can be deducedthat this is because of withdrawal of calcium from the bone, and henceosteoporosis is diagnosed.

For example, in the diagnostic apparatus recorded in Japanese UnexaminedPatent 2-104337 and U.S. patent application Ser. No. 193,295 the speedof sound in bony tissue is measured by radiating ultrasonic pulsestowards the bony tissue of an examinee which is the measurement sitefrom an ultrasound transducer on one side and receiving the ultrasonicpulses transmitted by the bone tissue at an ultrasound transducer on theother side, and progress in osteoporosis is diagnosed when the speed ofsound inside the bony tissue is slow. This is because this diagnosticapparatus acts on the premise that in experience the speed of sound inbony tissue is proportional to bone density.

However, the theoretical basis for linking bone density and the speed ofsound is not established: strictly speaking the speed of sound in bonytissue is given by the square root of "the elastic modulus of thebone/bone density" and is not proportional to bone density. Moreover,because the elastic modulus of bone rises as bone density increases sothat the modulus of elasticity of bone and bone density contribute tothe speed of sound in such a way that they cancel one another out, thespeed of sound in bony tissue cannot respond sensitively to an increasein bone density, and the coefficient of correlation between the speed ofsound in bony tissue and bone density is decidedly not high. Thetheoretical basis for a link between bone density and attenuation ofultrasound waves is also not established.

Therefore it is unreasonable to expect highly reliable diagnoses fromprior diagnostic apparatus which estimate bone density and the elasticmodulus of bone from the results of determination of attenuation ofultrasound waves and the speed of sound in bony tissue.

This invention is a response to the situation above, and its purpose isto offer a reflection type ultrasonic osteoporosis diagnosing apparatusand method which, despite being simple and offering no risk of radiationexposure, can estimate bone density or the elastic modulus of bone moreaccurately (sensitively) than this sort of prior device and method, andcan perform highly reliable diagnoses.

DISCLOSURE OF THE INVENTION

The osteoporosis diagnosing device of this invention diagnosesosteoporosis by setting an ultrasonic transducer against a certain skinsurface of an examinee and repeatedly radiating ultrasonic impulsestowards bone under the above skin while changing the direction of theemitting and receiving surface of the ultrasonic wave transducer withina certain range of solid angle which includes the line normal to thebone surface above, and for every pulse receiving by means of the aboveultrasonic transducer the echo returned from the bone surface, andconverting the received signal into a digital echo signal by means of ananalogue/digital converter, and performing digital signal processingusing the digital echo signals obtained by conversion.

Therefore, according to a 1st aspect of the osteoporosis diagnosingapparatus of this invention an osteoporosis diagnosing apparatus isoffered which is provided with an echo level detecting means whichdetects the echo level from the digital echo signal input above, and amaximum echo level extraction device which extracts the maximum echolevel from among a detected plurality of echo levels above, and adecision means which makes a decision as to osteoporosis based on themaximum echo level extracted above, and an output means which outputsthe results of the decision of the decision means.

In the 1st aspect of this osteoporosis diagnosing apparatus, there ispreferably an additional reflection coefficient calculating means whichcalculates the ultrasonic reflection coefficient of the bone relative tosoft tissue of the examinee based on the extracted maximum echo levelabove, or an acoustic impedance calculating means which calculates theacoustic impedance of the bone of the examinee. With these decisionmeans these can become able to make a decision on osteoporosis based onthe above ultrasonic reflection coefficient or acoustic impedance ofbone.

The reason is that the maximum echo level is a monotonically increasingfunction of the ultrasonic reflection coefficient, and the ultrasonicreflection coefficient is an monotonically increasing function of theacoustic impedance of bone, so that if any of the three increases (ordecreases) the other two will also show an accompanying increase (ordecrease). The acoustic impedance of bone can be expressed as the squareroot of (elastic modulus x density) of bone.

Consequently, with the constitution of this invention the acousticimpedance of bone (maximum echo level, ultrasonic reflectioncoefficient) receive the synergistic effects of a rise in elasticmodulus accompanying an increase in density; and therefore it respondsmore sensitively than the speed of sound with a marked increase. On theother hand, acoustic impedance is also affected synergistically by adecrease in density and a lowering of elastic modulus; and responds moresensitively than the speed of sound with a marked decrease. Consequentlythe acoustic impedance of bone is a good indicator for deciding bonedensity.

In calculating the ultrasonic reflection coefficient or the acousticimpedance of bone more accurate estimates can be obtained if it is alsopossible to take into account degree of attenuation in ultrasound wavesduring the round trip in soft tissues of the examinee, and hence this ispreferred.

In addition, according to a 2nd aspect of an osteoporosis diagnosingdevice of this invention, an osteoporosis diagnosing apparatus isoffered which diagnoses osteoporosis by setting against a certain skinsurface of an examinee the ultrasonic retarding spacer of an ultrasonictransducer fitted with an ultrasonic retarding spacer in order toeliminate the residual effect of the emitted signal at the emitting andreceiving surface of the ultrasonic oscillator, and repeatedly radiatingultrasonic impulses towards bone under the skin above while changing thedirection of the emitting and receiving surface of the ultrasonicoscillator within a certain range of solid angle which includes the linenormal to the bone surface above, and for every pulse receiving a 1stecho returned from the skin surface above, and then the 2nd echoreturned from the bone surface above, at the emitting and receivingsurface of the ultrasound wave oscillator above, and converting thereceived signal into 1st and 2nd digital echo signals by means of ananalogue/digital converter, and performing digital signal processingusing the 1st and 2nd digital echo signals obtained by conversion.

In addition, the method of diagnosing osteoporosis of this inventiondiagnoses osteoporosis by setting an ultrasonic transducer against acertain skin surface of an examinee and repeatedly radiating ultrasonicimpulses towards bone under the skin above, while changing the directionof the emitting and receiving surface of the ultrasonic transducerwithin a certain range of solid angle which includes the line normal tothe bone surface above, and for every pulse receiving the echo returnedfrom the bone surface by means of the ultrasonic transducer above anddetermining the echo level, and further extracting the maximum echolevel from among a determined plurality of echo levels above, andestimating bone density and the elastic modulus of the bone based on theextracted maximum echo level. The wave of maximum echo level is receivedwhen the line normal to the bone and the line normal to the emitting andreceiving surface of the ultrasonic transducer coincide, and at thistime vertical reflection from the bone is also vertically incident tothe emitting and receiving surface. When the line normal to the bone andthe line normal to the emitting and receiving surface coincide the echolevel is stable irrespective of greater or lesser deviation in thedirection of the emitting and receiving surface, so that measurementdata with good reproducibility are obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the electrical components of anosteoporosis diagnosing apparatus which is a 1st embodiment of thisinvention;

FIG. 2 is an outer view of the same apparatus;

FIG. 3 is a schematic drawing showing the mode of employment of the sameapparatus;

FIG. 4 is a flow chart showing the operating and processing routines ofthe same device;

FIG. 5 is a drawing used to explain the action of the same device;

FIG. 6 is also a drawing used in explaining the action of the samedevice;

FIG. 7 is a block diagram showing the electrical components of anosteoporosis diagnosing apparatus which is a 3rd embodiment of thisinvention;

FIG. 8 is a flow chart showing the operating and processing routines ofthe same device;

FIG. 9 is a block diagram showing the electrical components of anosteoporosis diagnosing apparatus which is a 4th embodiment of thisinvention; and

FIG. 10 is a flow chart showing the operating and processing routine ofan osteoporosis diagnosing apparatus which is a 6th embodiment of thisinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out this invention will be explained belowwith reference to the drawings. The explanation is in concrete termsusing embodiments.

The 1st Embodiment

FIG. 1 is a block diagram showing the electrical components of anosteoporosis diagnosing apparatus which is a 1st embodiment of thisinvention; FIG. 2 is an outer view of the same device; FIG. 3 is aschematic drawing showing the mode of employment of the same apparatus;FIG. 4 is a flow chart showing the operating and processing routines ofthe same device; FIG. 5 is a drawing used to explain the action of thesame device; FIG. 6 is also a drawing used to explain the action of thesame device.

As FIG. 1 to FIG. 3 show, the osteoporosis diagnosing apparatus of thisexample essentially comprises an ultrasonic transducer 1 (called simplya transducer hereafter), which when a half-wave impulse electricalsignal is input in a certain cycle, responds by radiating an ultrasonicimpulse Ai towards a certain bone Mb of an examinee at a measurementsite, and receives the echo (called bone echo hereafter) Ae returnedfrom the surface Y of the bone (cortical bone) Mb and converts it to areceived signal (electrical signal), and the body of the apparatus 2which feeds half-wave impulse electrical signals to the transducer 1,and performs the diagnosis of osteoporosis by extracting bone echolevels which are the amplitudes of the reflected waves from the bone Mbby processing the received signal above output from the transducer 1,and a cable 3 which connects the transducer 1 and the body of theapparatus 2.

The main component of the transducer 1 above is an ultrasonic oscillator1a having electrode layers on both sides of a thick disk-shapedoscillating type piezoelectric element of lead zirconate titanate (PZT),etc., and an ultrasonic retarding spacer 1b is affixed to one electrodesurface of this ultrasound oscillator 1a (the surface emitting andreceiving the ultrasonic impulses Ai) in order to eliminate the residualeffects of the emitted signal. When the residual emitted signal has noeffect on the received wave of the bone echo Ae the ultrasonic retardingspacer 1b can be omitted. In order to perform highly precisedeterminations here, it is desirable that unimpeded ultrasonic impulsesAi which can be regarded as plane waves from the emitting and receivingsurface of the transducer 1 can be radiated towards the bone Mb, andthat unimpeded bone echoes Ae which can be regarded as plane waves arereturned. Therefore, a transducer 1 in which the emitting and receivingsurface is made as wide as possible by constituting it with disk shapedpiezoelectric elements which have a comparatively large radius is ideal.From the same point of view, a bone Mb with a large radius of curvaturewhich can be regarded as a flat surface, and is close to the surface ofthe skin, such as the heel, the upper part of the knee cap or the shinis preferably made the measurement site.

The body of the apparatus 2 above is constituted by a pulse generator 4,a matching circuit 5, an amplifier 6, a waveform shaper 7, an A/Dconverter 8, a ROM 9, a RAM 10, a CPU (central processing unit) 11, alevel meter 12 and a display 13. The pulse generator 4 is connected tothe transducer 1 via the cable 3, and produces half-wave impulseelectrical signals of a central frequency of almost 2.5 MHz repeating ina certain cycle (e.g. 100 msec), which are sent to the transducer 1. Thematching circuit 5 matches impulses between the transducer 1 and thebody of the apparatus 2 connected via the cable 3 so that signals can besent and received with the maximum energy efficiency. Consequently, whenthe ultrasonic oscillator la of the transducer 1 receives a bone echo Aea received signal is output from the transducer 1, and is input to theamplifier 6 via the matching circuit 5 without any loss of energy. Theamplifier 6 amplifies received signals input through the matchingcircuit 5 to a certain amplitude, and then inputs them to the waveformshaper 7. The waveform shaper 7 comprises a band filter constituted byan LC, and filters received signals amplified by the amplifier 6,shaping the waveform into a linear shape from which the noise componentshould have been removed, and then inputs them to the A/D converter 8.The A/D converter 8 is provided with a sample holding circuit and asampling memory (SRAM), etc., and following a sampling start demand fromthe CPU 11 it samples input signals (waveform shaped analogue receivedsignals) output by the waveform shaper 7 at a certain frequency (e.g. 12MHz), and converts them sequentially to digital echo signals (calledbone echo signals hereafter), and after temporarily storing theresulting bone echo signals in its own sampling memory it issues them tothe CPU 11.

The ROM 9 houses the processing program, other than the operating system(OS), which the CPU 11 executes in order to diagnose osteoporosis. Thisprocessing program describes a routine for taking up a bone echo signalfrom the A/D converter 8 for every pulse and every echo and detectingthe bone echo level, a routine for extracting the maximum bone echolevel from among many echo bone levels thus detected, a routine forcalculating the ultrasonic reflection coefficient R of the bone Mb ofthe examinee relative to soft tissue Ma, and a routine for calculatingthe acoustic impedance Zb of the bone Mb of the examinee based on theultrasonic reflection coefficient R. In this treatment program theacoustic impedance Zb of the bone Mb of the examinee is given byEquation (1).

    Zb-Za(R+1)/(1-R)                                           (1)

Za: The acoustic impedance of soft tissue (already known)

When the surface Y of the bone Mb here is regarded as almost flat, andthe ultrasonic impulses Ai radiated from the transducer 1 are alsoregarded as being plane waves, and moreover the wave front thereof arealso regarded as almost parallel with the surface Y of the bone Mb (inother words when the ultrasonic impulses Ai are incident almostvertically at the surface Y of the bone Mb), the ultrasonic reflectioncoefficient R of the bone Mb of the examinee relative to soft tissue Macan be represented by Equation (2). In this connection, the bone echolevel is greatest when the ultrasonic impulse Ai is almost verticallyincident at the surface Y of the bone Mb. Therefore, the maximum echolevel extracted by this example, as will be discussed hereafter, isobtained when the ultrasonic impulses Ai are vertically incident at thesurface Y of the bone Mb, and hence the ultrasonic reflectioncoefficient R calculated from the extracted maximum echo levelcorresponds to the ultrasonic reflection coefficient R given by Equation(2). Equation (1) is obtained by transforming Equation (2).

    R=(Zb-Za)/(Zb+Za)                                          (2)

The RAM 10 has a working area designated as the working area for the CPU11, and a data area where data are temporarily stored; in the data areathere is an echo data memory area which stores the bone echo leveldetected in the current run (current-run bone echo level) and themaximum bone echo level extracted from the bone echo levels detected upuntil the current run, and a waveform memory area which stores the boneecho waveform of the wave received in the current run and the waveformof the wave received when the maximum bone echo level was detected(maximum bone echo waveform), and a continuation of measurement flagwhich stores information on whether or not measurement is continuing,etc.

By executing the processing programs mentioned above which are stored inthe ROM 9, using the RAM 10, the CPU 11 controls each component of theapparatus starting with the pulse generator 4 and the A/D converter 8,and for every single wave pulse and echo takes up a bone echo signalfrom the A/D converter 8, detects the echo level then extracts themaximum echo level from among them, and calculates the ultrasonicreflection coefficient R of the bone Mb of the examinee relative to softtissue Ma on the basis of the value of the extracted maximum echo level,and performs the diagnosis of osteoporosis by calculating the acousticimpedance Zb of the bone Mb of the examinee based on the calculatedultrasonic reflection coefficient R.

The level meter 12 is controlled by the CPU 11 and displayssimultaneously the current-run bone echo level stored in the RAM 10 asthe deflection of a liquid crystal needle pattern 12a shown in thebroken line in FIG. 2 and FIG. 3, and the maximum echo level detected todate (up to the current run) as the deflection of a liquid crystalneedle pattern 12b shown by the solid line in the same drawings. Thedisplay 13 comprises a CRT display or liquid crystal display, etc.,which is controlled by the CPU 11 and displays on a screen the maximumbone echo level (measured value), the ultrasonic reflection coefficientR (calculated value), the acoustic impedance Zb (calculated value), thecurrent-run bone echo waveform and the maximum bone echo waveform, etc.

Next, the operation of this example will be explained with reference toFIG. 3 to FIG. 6 (primarily the flow of CPU 11 processing whendiagnosing osteoporosis).

Firstly, cortical bone of a bone Mb with a large radius of curvature,close to the skin surface, such as the heel, the upper knee cap or theshin bone, etc., is selected as a measurement site. These are preferredbecause unimpeded bone echoes Ae which can be regarded as plane wavesare returned from such bone Mb, and hence precision is higher. The powersource is plugged into the apparatus, and the CPU 11 resets each of thecomponents of the apparatus, and initializes counters, resistors andflags (Step SP10 (FIG. 4)); and then the switch for the start ofmeasurement is pushed down (SP11). As FIG. 3 shows, here the operatorsmears an ultrasonic gel 14 on the surface of soft tissue Ma (skinsurface X) covering the bone Mb which is the measurement site in theexaminee, sets the transducer 1 against the surface of the skin X viathe ultrasonic gel 14 with the emitting and receiving surface towardsthe bone Mb, and switches the start of measurement switch ON. Once thestart of measurement switch has been turned ON, (Step SP11), the CPU 11writes 1! to the continuation of measurement flag, and after setting upthe continuation of measurement flag, this starts diagnostic operationfollowing the processing routines shown in FIG. 4.

The CPU 11 first issues a 1 pulse generation command to the pulsegenerator 4 (Step SP12). When the pulse generator 4 receives the 1 pulsegeneration command from the CPU 11, it sends a half-wave impulseelectrical signal to the transducer 1. On receiving the half-waveimpulse electrical signal fed from the pulse generator 4, the transducer1 radiates an ultrasonic impulse Ai towards the bone Mb of the examinee(which can be regarded as an unimpeded plane wave over the shortdistance handled). As shown in FIG. 5, the radiated ultrasonic impulseAi is partially reflected at the surface of the skin X, and theremainder enters soft tissue Ma from the surface of the skin X andpropagates towards the bone Mb. Part is then reflected at the surface ofthe bone Mb and becomes the bone echo Ae, part is absorbed by the boneMb, and the remainder is transmitted by the bone Mb. The bone echo Aepasses along the reverse path to the incident ultrasonic wave, and isreceived again by the ultrasonic oscillator 1a of the transducer 1.

Consequently, after radiating the ultrasonic impulse Ai, the ultrasonictransducer 1 receives first the residual sound of the emitted signal An,then the echo from the surface of the skin (called the surface echohereafter) As, and then slightly later the bone echo Ae by means of theultrasonic oscillator 1a, and these are converted to received signals ofcorresponding ultrasonic waveforms and amplitudes. The received signalsthat are produced are input via the cable 3 to the body of the apparatus2 (matching circuit 5), amplified to a desired amplitude by theamplifier 6, and after being shaped to a linear waveform by the waveformshaper 7 they are input to the A/D converter 8.

After the CPU 11 has emitted the 1 pulse generation command to the pulsegenerator 4 (Step SP12), it times the time for the bone echo Ae to bereturned to the emitting and receiving surface of the ultrasonicoscillator la of the transducer 1 after the residual sound of theemitted signal has been received by the ultrasonic oscillator la of thetransducer 1 and then the surface echo As has been received, and issuesa start of sampling command to the A/D converter 8 (Step S13). Onreceiving the start of sampling command from the CPU 11, the A/Dconverter 8 samples the received signals of each individual echo fromthe bone Mb which are input from the waveform shaper 7 after shaping thewaveform, at a certain frequency (e.g. 12 MHz), converts them to digitalsignals, and temporarily stores the resulting N sample values (digitalsignals for single echoes) in its own sampling memory. It subsequentlyissues the N sample values stored in the sampling memory in sequence tothe CPU 11, in accordance with transfer orders from the CPU 11.

The CPU 11 takes up the N sample values in sequence from the A/Dconverter 8, and after recording in the waveform memory area of the RAM10 as the current-run bone echo waveform, the current-run bone echolevel (current-run bone echo amplitude) is detected by extracting thehighest value from among the N sample values, and the result ofdetection is stored in the echo data memory area of the RAM 10 (StepSP14). The current-run bone echo level stored in the RAM 10 is displayedas the deflection of a liquid crystal needle pattern 12a on the levelmeter 12 as shown by the broken line in FIG. 3 (Step SP15).

Then the CPU 11 reads out the current-run bone echo level and themaximum bone echo level from the echo data memory area inside the RAM10, and decides whether or not the value of the current-run bone echolevel is larger than the value for maximum bone echo level (Step SP16).Since this is the initial decision the value for the maximum bone echolevel is still the initial value 0!, and so the CPU 11 decides that thevalue of the current-run bone echo level is greater than the value ofthe maximum bone echo level, and the value of the maximum bone echolevel stored in the echo data memory area of the RAM 10 is rewritten tothe value of the current-run bone echo level, and the maximum bone echowaveform recorded in the waveform memory area of the RAM 10 is rewrittento the current-run bone echo waveform (Step SP17). The updated maximumbone echo waveform is displayed on the screen of the display 13, and theupdated maximum bone echo level is displayed as a deflection of a liquidcrystal needle pattern 12b on the level meter 12, as shown by the solidline in FIG. 3 (Step SP18).

Then the CPU 11 checks for the continuation of measurement flag in theRAM 10 (Step SPl9) and if the continuation of measurement flag isstanding (when the content of the continuation of measurement flag is1!) the CPU 11 decides to continue measurement, and after repeating theprocedure for radiating 1 pulse and receiving 1 echo (Steps SP12-SP15),in Step 16 it again reads out the current-run bone echo level and themaximum bone echo level from the echo data memory area in the RAM 10,and decides whether or not the current-run bone echo level value isgreater than the maximum echo level value. When the current bone echolevel is not larger than the maximum bone echo level the result of thisdecision is to go directly to Step SP19 without performing an update,and to check for the continuation of measurement flag. The content ofthe continuation of measurement flag remains 1! as long as the operatordoes not push the end of measurement switch and the CPU repeats theoperations of radiating 1 pulse and receiving 1 echo (Steps SP12-SP15)and extracting the maximum bone echo level (Steps SP16-SP19).

While the CPU 11 repeats the process described above (Steps SP12-SP19),the operator changes the direction of the transducer 1 so that whileremaining on the surface of the skin X and directed towards the bone Mbof the site of measurement, the direction of the transducer 1 ischanged, sometimes in a circle or spiral as in the precession of comaabberation, and sometimes inclining it from back to front or right toleft in a seesaw motion as shown in FIG. 3, changing the angle, toinvestigate the direction in which the maximum deflection of the liquidcrystal needle patterns 12a and 12b of the level meter 12, i.e. themaximum bone echo level, is detected. As FIG. 6(a) shows, thedeflections of the liquid crystal needle patterns 12a and 12b of thelevel meter 12 are largest when the line normal to the bone Mb coincideswith the line normal to the emitting and receiving surface of thetransducer 1; and therefore, when the wave front of the plane waveultrasonic impulse Ai is almost parallel to the surface Y of the bone Mb(i.e. when the plane wave ultrasonic impulse Ai is almost verticallyincident at the surface Y of the bone Mb).

This is because, as the same drawing (a) shows, then both normal linescoincide the bone echo Ae reflected vertically by the surface Y of thebone Mb returns vertically to the emitting and receiving surface of thetransducer 1, and consequently the wave front of the bone echo Ae isaligned almost parallel with emitting and receiving surface of thetransducer 1 so that there is the minimum of phase deviation of the boneecho due to a difference in the position at which it received by theemitting and receiving surface, and there is little interference betweencrests and hollows of received signals, and therefore the bone echo Aeof the maximum bone echo level is received. By contrast, when the twonormal lines do not coincide, as the same drawing (b) shows, the wavefronts of the bone echo Ae are unaligned at the emitting and receivingsurface, so that interference between crests and hollows diminishes thereceived signal. For this reason, when the bone echo level peaks as theoperator changes the angle of the transducer 1 in the vicinity of theline normal to the bone Mb it can be reckoned that the reflected boneecho Ae has been returned almost vertically to the emitting andreceiving surface of the transducer 1 by the surface Y of the bone Mb.

The important thing here is that in the diagnostic apparatus of thisinvention in order to raise precision it is necessary to extract thevertically reflected bone echo Ae. This is because Equation (1) whichleads to the acoustic impedance of the bone, as mentioned above, is theequation which holds for an almost vertically reflected bone echo Ae.However, it is not difficult to extract the perpendicularly reflectedecho: the vertically reflected echo can be discovered easily byobserving the deflections of the liquid crystal needle patterns 12a and12b of the level meter 12. In other words, when the non-coincidence ofthe line normal to the bone Mb and the line normal to the emitting andreceiving surface of the transducer 1 is extreme the liquid crystalneedle patterns 12a and 12b of the level meter show sensibledeflections, so that extreme non-coincidence between the two normallines can be recognized; on the other hand, when the two normal linesare close to coincidence the bone echo level is stable to deviations inthe direction of the emitting and receiving surface of the transducer 1and the deflections of the liquid crystal needle patterns fall, enablingrecognition of coincidence of the two normal lines.

The operator watches the deflections of the liquid crystal needlepatterns 12a and 12b of the level meter 12, and when it is judged thatthe maximum bone echo level has been extracted he/she pushes down theend of measurement switch. Once the end of measurement switch has beenpressed down, the CPU 11 writes the content of the continuation ofmeasurement flag to 0! by an interruption process, and the continuationof measurement flag goes down. Once the continuation of measurement flaggoes down, the CPU 11 stops the radiation of subsequent pulses (StepSPl9). The maximum bone echo level recorded in the echo data memory areaof the RAM 10 is then read out, and displayed on the panel of thedisplay 13 (Step SP20).

After this, the CPU 11, calculates the ultrasonic reflection coefficientR of the interface between soft tissue Ma and bone Mb of the examineefrom the maximum bone echo level Ve stored in the echo data memory areaof the RAM 10, and the total echo level V0 previously stored in ROM byexecuting the reflection coefficient calculation routine (Step SP21),and displays the calculated value on the panel of the display 13 (StepSP22).

The ultrasonic reflection coefficient R here is derived from the ratioof the total echo level V0 and the maximum bone echo level Ve when thereflection is completely vertical (R=Ve/V0 ); the total echo level canbe calculated theoretically, but it is also possible to find it byradiating an ultrasonic impulse towards air and determining the openecho level when the open echo returned from the end face of anultrasonic retarding spacer (dummy block) 1b of polyethylene bulk, etc.,is received by the ultrasonic oscillator 1a. Then, the CPU 11,calculates the acoustic impedance Zb (kg/m². sec) of the bone Mb byexecuting the acoustic impedance calculating routine, by substitutinginto Equation (1) the value for the ultrasonic reflection coefficient Rgiven by the reflection coefficient calculating routine (Step SP23), anddisplays the result of the calculation on the panel of the display 13(Step SP24).

With the constitution above, when the line normal to the bone and theline normal to the emitting and receiving surface almost coincide theecho level is stable to greater or lesser deviations in the direction ofthe emitting and receiving surface (the deflection of the liquid crystalneedle patterns 12a and 12b of the level meter falls), and therefore thebone echo level during vertical reflection, i.e. maximum bone echo canbe easily extracted, and moreover, measurement data can be obtained withgood reproducibility. In addition, the fact that the maximum bone echolevel is also shown as a fixed value on the level meter 12 as long as itis not updated, in addition to the current bone echo level, makes iteven more easy to investigate the maximum bone echo level. Therefore,the acoustic impedance Zb of the bone Mb can be found with goodprecision.

The acoustic impedance Zb of the bone Mb is represented by the squareroot of (elastic modulus×density! of the bone Mb, and hence if bonedensity increases and elastic modulus also rises it is synergisticallyaffected and responds more sensitively than the speed of sound, with amarked increase. On the other hand if bone density decreases and elasticmodulus is also lowered, acoustic impedance is synergistically affectedand responds more sensitively than the speed of sound with a markeddecrease. Consequently, the acoustic impedance Zb of the bone Mb becomesa good indicator for judging bone density. Therefore, from the value foracoustic impedance of the bone Mb displayed on the display 13 theoperator can estimate accurately the situation as far as the progress ofosteoporosis is concerned. For example, when the acoustic impedance isconsiderably smaller than the average value for the age group it isevident that there has been a deterioration in osteoporosis in the boneMb.

In addition, since only the bone echo level detected in the current runand the maximum bone echo level are stored in the echo data memory areaof the RAM 10 and echo levels detected previously are erased unless theyare the maximum echo level, a cheap RAM with a small memory capacity canbe employed. Of course, a RAM with a large memory capacity can also beused, with all of the bone echo levels detected during the entiremeasurement period being temporarily stored and the maximum bone echolevel being extracted after finishing the measurements from among all ofthe echo levels recorded in the RAM.

The 2nd Embodiment

A 2nd embodiment of this invention will next be explained.

This 2nd embodiment has almost the same constitution as the 1stembodiment, except for the adoption of an algorithm for calculating theultrasonic reflection coefficient which is different from the 1stembodiment discussed above.

In the 2nd embodiment the ultrasonic reflection coefficient R of thebone Mb relative to soft tissue Ma is given by Equation (3), when theultrasonic impulse Ai and the bone echo Ae can be regarded as adequatelyplane waves and the attenuation of ultrasound waves by soft tissue Macan be ignored.

    R=Ve/p·Q·B·Vi                   (3)

p: The sound pressure of the ultrasonic impulse output in an almostvertical direction from the emitting and receiving surface of thetransducer 1 when a unit electrical signal (voltage, current, scatteringparameter) is applied to the transducer 1

Q: The amplitude of the received signal (electrical signal) output fromthe transducer when an echo of a unit sound pressure is verticallyincident at the emitting and receiving surface of the transducer

B: The product of degree of amplification of the amplifier 6 and degreeof increase in amplification of the waveform shaper 7

Vi: The amplitude of the electrical signal (voltage, current, scatteringparameter) applied to the transducer 1 from the pulse generator 4

Ve: The maximum bone echo level

It should be noted that P, Q, B and Vi are all functions of frequency,and here a component at a central frequency (e.g. 2.5 MHz) is used. Asfar as P, Q, B and Vi are concerned, the measured values and set valuesfor these are written beforehand into the ROM 9.

Equation (3) is derived as follows. Firstly, when an electrical signalof amplitude Vi is applied to the transducer 1 from the pulse generator4, an ultrasonic impulse of sound pressure PVi is output from theemitting and receiving surface of the transducer 1 towards the bone Mb.Consequently, a bone echo Ae of sound pressure RPVi is returnedvertically to the emitting and receiving surface of the transducer 1.Therefore, the maximum bone echo level Ve is given by Equation (4).

    Ve=Q·R·P·B·Vi          (4).

Rearrangement of this Equation (4) gives Equation (3).

Since the acoustic impedance Zb of the bone Mb is thus also calculatedby the CPU 11 from the ultrasonic reflection coefficient R in the 2ndembodiment, almost the same benefits can be obtained as in the 1stembodiment.

The 3rd Embodiment

FIG. 7 is a block diagram showing the electrical components of anosteoporosis diagnosing apparatus which is a 3rd embodiment of thisinvention; and FIG. 8 is a flow chart showing the operating andprocessing routines of the same apparatus.

The big difference between this 3rd embodiment and the 2nd embodimentdiscussed above is that the acoustic impedance Zb of the bone Mb can bedetermined with certainty by considering degree of attenuation ofultrasound waves A(T) due to the round trip through soft tissues Ma.

To this end, as FIG. 7 shows, the body of the apparatus 2 of thisexample has an additional timing circuit 14 which measures the bone echoarrival time T after an ultrasonic impulse Ai has been radiated from theemitting and receiving surface of the transducer 1 for the bone echo Aeto be returned to the emitting and receiving surface. In addition, theprocessing program of this example includes the description of a routinefor calculating the ultrasonic reflection coefficient R of the bone Mbrelative to soft tissue Ma of the examinee based on the maximum boneecho level extracted by a similar algorithm to that in the 1stembodiment and the bone echo arrival time T at that time; the CPU 11calculates the ultrasonic reflection coefficient R by executing theprocessing program, and a diagnosis of osteoporosis is performed basedon the calculated ultrasonic reflection coefficient R. In other pointseach of the component parts are the same as in FIG. 1, so thesecomponent parts are labelled in the same way as component parts shown inFIG. 1, and the explanation thereof is omitted.

In the body of the apparatus 2a of this example, the pulse generator 4aresponds to pulse generation commands from the CPU 11 repeated at in acertain cycle, and produces half-wave impulse electrical signals of acentral frequency of almost 2.5 MHz in the certain cycle; and as well assending a signal to the transducer 1 it feeds a start of timing signalTp to the timing circuit 4 with the same timing as the half-wave impulsesignal.

The cycle of the half-wave impulse here is set at a sufficiently longertime than the bone echo arrival time T. The timing circuit 14 isconstituted by a clock generator and a counting circuit, not shown inthe drawings: timing is started the moment that a start of timing signalTp fed from the pulse generator 4 is received, and timing is finishedwhen

the final signal is received from the A/D converter 8a. The time valueis held until it is reset, and the held time value is given to the CPU11 as the bone echo arrival time in accordance with demands.

The operation of this example (mainly CPU 11 processing flow whendiagnosing osteoporosis) will next be explained with reference to FIG.8. In the processing flow in this example Step SP10 to Step SP20, exceptfor the measurement of the bone echo arrival time T, are almost the sameas discussed in the 1st embodiment and so they will only be explainedbriefly.

In this example, when the CPU 11 reads in a bone echo signal E from theA/D converter 8a in Step SP14 it also reads the bone echo arrival time Tfrom the timing circuit 14 and stores in the echo data memory area ofthe RAM 10 the current bone echo signal E and the bone arrival time Twhich have been read in.

After measurement has finished (Step SPl9, Step SP20), the CPU 11 firstcalculates degree of ultrasonic attenuation A(T) in soft tissues Ma ofthe examinee by executing an ultrasonic attenuation calculation routine,reading out the bone echo arrival time T from the echo data memory area,substituting the read-out value for the bone echo arrival time T(sec)into Equation (5) (Step SP201). ##EQU1## Degree of attenuation A(T) hereis degree of attenuation in the ultrasonic wave in the round trip withinsoft tissues Ma: thus, it means degree of attenuation in the ultrasonicwave during its propagation from the surface of the skin X to thesurface Y of the bone Mb and reflection by the surface Y of the bone Mbuntil it is returned again to the surface of the skin Y (the smallerA(T) the greater degree of attenuation). This attenuation A(T) is afunction of bone echo arrival time; the equation of the function can befound by experiment or simulation. Ultrasonic waves are attenuated insoft tissues because: 1. the ultrasonic waves employed in this exampleare probably not completely plane waves but include a spherical wavecomponent, and acoustic energy is diffused by this spherical wavecomponent (ultrasonic diffusion); and 2. acoustic energy is convertedinto heat energy by friction with soft tissues Ma (ultrasonicabsorption). Degree of attenuation caused by ultrasonic diffusion can befound by calculation or experiment from the opening of the transducer 1,the frequency of the ultrasonic waves and the speed of sound in softtissues Ma. Degree of attenuation due to ultrasonic absorption becomessmaller if the ultrasonic frequency is lowered, and if the frequency ismade low enough an absorption constant typical of soft tissue Ma(percentage ultrasonic attenuation per unit length) can be used. Inpassing, Equation (5) which gives degree of ultrasonic attenuation A(T),is an experimental equation established when the central frequency ofthe ultrasonic waves employed was set to 2.5 MHz, and the opening of thetransducer was set to 15 mm.

The CPU 11 next reads out the maximum bone echo level Ve from the echodata memory area, substitutes this together with degree of attenuationA(T) calculated using Equation (5) into Equation (6), and calculates theultrasonic reflection coefficient R at the interface between soft tissueMa and the bone Mb when the ultrasonic wave is vertically incident atthe bone Mb from the medium of soft tissue Ma (Step SP21).

    R=Ve/P·Q·B·Vi·A(T)     (6)

The meanings of P, Q, B and Vi are the same as mentioned in Equation(3). Equation (6) is derived as follows.

Firstly when an electrical signal of amplitude Vi is applied to thetransducer 1 from the pulse generator 4a, an ultrasonic pulse Ai ofsound pressure PVi is injected into soft tissues Ma from the emittingand receiving surface of the transducer 1. The injected ultrasonic pulseAi attenuated inside soft tissues Ma is reflected vertically by thesurface Y of the bone Mb (considering the case when it is verticallyincident at the surface Y of the bone Mb), and becomes a bone echo Aewhich is returned vertically to the transducer 1.

Consequently, the sound pressure P(e) of the bone echo Ae returnedvertically to the emitting and receiving surface of the transducer 1,taking into account degree of attenuation A(T) of the ultrasound wave bythe round trip in soft tissues Ma found by Equation (5), is given byEquation (7).

    p(e)=P·Vi·R·A(T)                (7)

When the bone echo Ae of sound pressure P(e) is received at the emittingand receiving surface of the transducer 1, the transducer 1 outputs areceived signal of amplification Q.P(e), and this received signal isamplified in the amplifier 6 (and the waveform shaper 7) by a degree ofamplification B. After digital conversion by the A/D converter 8a, it istaken up by the CPU 11, and detected as a maximum bone echo level

    Ve(=B·Q·p(e)).

Consequently, the maximum bone echo level Ve is given by Equation (8).

    Ve=P·Vi·R·A(T)·B·Q(8)

Isolating the ultrasonic reflection coefficient R from Equation (8)gives Equation (6).

To return again to the explanation of the flow chart of FIG. 8, aftercalculating the ultrasonic reflection coefficient R at the interfacebetween soft tissues Ma and the bone Mb by using Equation (6) (StepSP21), the CPU 11 displays the calculated result on the display 13 (StepSP22).

After this, the CPU 11 calculates the acoustic impedance Zb (N.s/m³) ofthe bone Mb using Equation (1) (Step SP23), and displays the calculatedresult on the display 14 (Step SP24).

With the constitution, in addition to the benefits of Embodiment 1discussed above it is possible to determine the acoustic impedance ofthe bone Mb with a greater degree of accuracy, since degree ofattenuation A(T) of the ultrasonic wave due to the round trip in softtissues Ma is taken into account.

The 4th Embodiment

FIG. 9 is a block diagram of the electrical components of anosteoporosis diagnosing apparatus which is a 4th embodiment of thisinvention.

In this 4th embodiment the fact that degree of attenuation A(T) of theultrasonic wave due to the round trip in soft tissues Ma is consideredis the same as in the 3rd Embodiment discussed above; however, itdiffers from the 3rd embodiment discussed above in that the surface echoAs produced by the contact surface X of an ultrasonic retarding spacer1b with the skin is received, the level thereof (surface echo level) isdetected, and degree of attenuation A(T) is calculated based on thedetected surface echo level.

Thus, in the body of the apparatus 2b in this example the A/D converter8b digitalizes in sequence the signal received first after the start ofsampling (the received signal relating to the surface echo As) and thesignal received next (the received signal relating to the bone echo Ae)as a surface echo signal Es and a bone echo signal Ee, by sampling theinput signals output by the waveform shaper 7 (waveform-shaped analoguereception waves) with a set frequency (e.g. 12MHz) following the demandfor the start of sampling from the CPU 11, and after storing the surfaceecho signal Es and bone echo signal Ee obtained by this conversiontemporarily in its own sampling memory, they are issued to the CPU 11 inaccordance with demands. The A/D converter 8b also produces a surfaceecho arrival signal Ts when the surface echo As is received, and thenproduces a bone echo arrival signal Te when the bone echo Ae isreceived, and gives these to a counting circuit 14b.

The timing circuit 14b is constituted by a clock generator and acounting circuit not shown in the drawings: when a surface echo arrivalsignal Ts fed from the A/D converter 8b is received, the countingcircuit is reset and timing is started; and when the bone echo arrivalsignal Te is received the counting circuit is ended. The time value isheld until it is reset, and the time value held is given to the CPU 11as the bone echo arrival time T in accordance with demands. The boneecho arrival time T here means the delay between the arrival of the boneecho Ae and a base time (the time of arrival of the surface echo As),and the value obtained by multiplying the bone echo arrival time T bythe speed of sound in soft tissues Ma corresponds to twice the thicknessof soft tissues: i.e. the distance of the round trip of the ultrasonicwave in soft tissues.

The processing program of this example comprises a processing routinealmost the same as that described in the 1st embodiment, but theultrasonic reflection coefficient R is given by Equation (9).

    R= (Za+Zc)·(Za-Zc)·Ve!/ 4Za·Zc A(T)·Vs!(9)

Zc: The acoustic impedance of the ultrasonic retarding spacer 1b(measured value or calculated value already known)

Za: The acoustic impedance of soft tissues Ma (measured value orcalculated value already known)

Ve: The maximum echo level

Vs: The surface echo level when the maximum echo level is received

T: The bone echo arrival time when the maximum echo level is received

A(T): Degree of ultrasonic attenuation when the maximum echo level isreceived.

Equation (9) is derived as follows.

Firstly, when a half-wave impulse electrical signal (amplitude Vi) issent to the transducer 1 from the pulse generator 4 the transducer 1radiates an ultrasonic impulse Ai towards the bone Mb of the examineefrom the emitting and receiving surface of the ultrasonic oscillator 1a.If the sound pressure of the ultrasonic impulse Ai output from thetransducer at the end surface of the ultrasonic retarding spacer 1b is Pwhen a unit electrical signal (voltage, current, scattering parameter,etc.) is applied to the transducer, the ultrasonic impulse Ai reachesthe end surface of ultrasonic retarding spacer 1b with a sound pressureof PVi; here the majority enters soft tissues Ma from the surface of theskin X, but a part becomes surface echo As, and is received again by thetransducer 1 along the reverse path.

The sound pressure P(s) of the surface echo As is given by Equation(10).

    P(s)=D·P·Vi                              (10)

where

    D=(Za-Zc)/(Za+Zc)

D: The ultrasonic reflection coefficient at the interface of theultrasonic retarding spacer 1b and soft tissue Ma when the ultrasonicwave is vertically incident to soft tissue Ma from the ultrasonicretarding spacer 1b

Now, if the amplitude of the received signal (electrical signal) outputfrom the transducer 1 is Q when an echo of a unit incident soundpressure is incident vertically at the end surface of the ultrasonicretarding spacer 1b , the transducer 1 outputs a received signal ofamplitude Q.P(s) when the surface echo As of the sound pressure P(s) isreceived at the ultrasound oscillator 1a of the transducer 1. Thisreceived signal is amplified by the amplifier 6 and the waveform shaper7, and is digitalized by the A/D converter 8b as a surface echo signalEs. Consequently, if the product of the amplitude amplification of theamplifier 6 and the amplitude amplification of the waveform shaper 7 isB, the surface echo level Es is given by Equation (11).

    Es= (Za-Zc)/(Za+Zc)!·B·Q·P·Vi(11)

On the other hand, the ultrasonic impulse Ai of sound pressure PVi isinjected into soft tissues Ma from the end surface of the ultrasonicretarding spacer 1b (skin surface Y) with a sound pressure of PVi.T12.T12 here is the percentage transmittance of ultrasonic sound pressurevertically incident from the medium of the ultrasonic retarding spacer1b to the medium of soft tissue Ma. When the ultrasonic impulse Ai ofsound pressure PVi.T12 injected into soft tissues Ma is verticallyincident at the bone surface Y, it forms a bone echo Ae which isvertically reflected at the bone surface Y and returned to thetransducer 1. The sound pressure F(e) of the bone echo Ae returnedvertically to the emitting and receiving surface of the ultrasonicoscillator la, considering degree of ultrasonic attenuation A(T) due tothe round trip in soft tissues Ma, is given by Equation (12). It shouldbe noted in passing that the component reflected when the ultrasonicwave is incident on the ultrasonic retarding spacer 1b from the mediumof soft tissue Ma, and the component of attenuation inside theultrasonic retarding spacer 1b, are ignored.

    P(e)=P·Vi·T12·T21·R·A(T)

where

T21: The percentage transmittance of the ultrasound wave incidentvertically from the medium of soft tissue Ma to the medium of theultrasonic retarding spacer 1b

When the bone echo Ae of sound pressure P(e) is received vertically atthe ultrasonic oscillator 1a of the transducer 1, the transducer 1outputs a received signal of amplitude Q.P(e). This reception signal isamplified by the amplifier 6 (and the waveform shaper 7) by a degree ofamplification B, and digitalized by the A/D converter as the maximumbone echo signal.

Consequently, the maximum bone echo level Ve is given by Equation (13).

    Ve=P·Vi·T12·T21·R·A(T).multidot.B·Q                                             (13)

The transmittance T12 of sound pressure from the ultrasonic spacer 1b tosoft tissue Ma here is given by Equation (14).

    T12=2Zc/(Za+Zc)                                            (14)

Similarly, the transmittance T21 of sound pressure from soft tissue Mato the ultrasonic retarding spacer 1b is given by Equation (15).

    T21=2Za/(Za+Zc)                                            (15)

Rearranging Equation (13) using Equations (14) and (15), the maximumbone echo level is given by Equation (16).

    Ve=P·Vi·R·A(T)·B·Q·4Za·Zc/(Za+Zc).sup.2                                (16)

On substituting Equation (16) into Equation (11), Equation (17) isobtained.

    Ve=R·A(T)·Vs·4Za·Zc/ (Za+Zc)·(Za·Zc)!                                           (17)

Vs in Equation (17) here is the surface echo level when the maximun echolevel Ve is received; Equation (17) can be rearranged to give Equation(19) above, which gives the ultrasonic reflection coefficient R in thisexample.

In this constitution the CPU 11, by executing the processing programabove stored in the ROM 9, using the RAM 10, takes up the surface echosignal Es and bone echo signal Ee from the A/D converter 8b for eachpulse and echo and detects the surface echo level and the bone echolevel by following an algorithm almost the same as in the 1stembodiment, then extracts the maximum bone echo level Ve from amongthem, calculates the ultrasonic reflection coefficient R given byEquation (9) based on the extracted maximum bone echo level Ve, thesurface echo level Vs at this time and the bone echo arrival time T atthis time, calculates the acoustic impedance of the bone of the examineebased on the ultrasonic reflection coefficient R, and makes a diagnosisas to osteoporosis using the calculated acoustic impedance of the boneas an index.

The constitution above can also give almost the same benefits mentionedin the 3rd embodiment.

The 5th embodiment

Degree of attenuation A(T) of the ultrasonic wave due to the round tripin soft tissue Ma is also considered in this 5th embodiment. Thehardware components of this example are almost the same as those if the4th embodiment (FIG. 9), but software components, i.e. the algorithmsfor calculating the ultrasonic reflection coefficient and the acousticimpedance of the bone Mb are different from the 4th embodiment mentionedabove.

Thus, in this embodiment the ultrasonic reflection coefficient R at softtissue Ma/bone Mb interface is given by Equation (18).

    R=h/ (1+s)·(1-s)·A(T)!                   (18)

where

    h=Ve/p·Q·B·Vi

    s=Vs/P·Q·B·Vi

Where the meanings of P, Q, B and Vi are the same as mentioned inEquation (3). The acoustic impedance Za of soft tissue Ma is given byEquation (19), rearranging Equation (11).

    Za=(1+s)/(1-s)·Zc                                 (19)

where

    s=Vs/P·Q·B·Vi

Equation (18) is derived from Equation (19) and Equation (16).

Similarly, the acoustic impedance Zb of the bone Mb is given by Equation(20).

    Zb=Zc·(1+s)/(1-s)·(1+R)/ (1-R)           (20)

where

    s=Vs/P·Q·B·Vi

The constitution above can also give almost the same benefits mentionedin the 4th embodiment.

The 6th embodiment

FIG. 10 is a flow chart showing the operating and processing routines ofan apparatus for diagnosing osteoporosis which is a 6th embodiment ofthis invention.

This 6th embodiment has in common with the 4th embodiment and the 5thembodiment mentioned above the fact that degree of attenuation A(T) ofultrasonic waves due to the round trip in soft tissue Ma is considered,and the fact that the hardware components are almost the same; howeverit differs from the previous two embodiments in that a pre-measurementroutine is executed before executing the main measurement routine forthe purpose of diagnosing osteoporosis.

As FIG. 10 shows, in the pre-measurement routine an ultrasonic impulseAi is radiated toward air (Step SQ12), and the open time echo returnedfrom the end surface of an ultrasonic retarding spacer 1b such aspolyethylene bulk, etc., at this time is received by the ultrasonicoscillator la (Step SQ13) and the opening time echo level V0 is measured(Step SQ16). After this, the main measurement routine is executed (StepSQ18). In the main measurement routine, processing is executed accordingto almost the same flow as explained in the 4th embodiment.

In this embodiment the ultrasonic reflection coefficient R of the boneMb of the examinee relative to soft tissue Ma is given by Equation (21).

    R=h/ (1+s)·(1-s)·A(T)!                   (21)

where

    h=-Ve/V0

    s=-Vs/V0

Ve: The maximum bone echo level

Vs: The surface echo level when the maximum bone echo level is received

T: The bone echo arrival time when the maximum bone echo is received

A(T) Degree of ultrasonic attenuation when the maximum bone echo levelis received

V0: The open time echo level

Equation (21) is derived as follows.

Firstly, when the sound pressure of the ultrasonic impulse Ai incidenton the medium of air from the medium of the ultrasonic wave retardingspacer 1b is Pi, the sound pressure P(0) of the opening echo A0 producedat the interface of the ultrasonic wave retarding spacer 1b and air isgiven by Equation (22).

    D0=P(0)/Pi=(Z0-Zc)/(Z0+Zc)                                 (22)

where

Zc: The acoustic impedance of the ultrasonic wave retarding spacer 1b(known)

Z0: The acoustic impedance of air

D0: The reflection coefficient of sound pressure at the interface of theultrasonic wave retarding spacer 1b and air when the ultrasound wave isvertically incident to air from the medium of the ultrasonic waveretarding spacer 1b

In this connection, considering the fact that Zc is almost 10⁴ times Z0,Z0/Zc can be taken as tending to 0, so that Equation (23) is obtainedfrom Equation (22).

    P(0)=-Pi                                                   (23)

Below, it is possible to arrive at Equation (21) by following almost thesame process as in the 5th embodiment.

Similarly, in this embodiment the impedance Zb of the bone Mb of theexaminee is given by Equation (24).

    Zb=Zc· (1+s)/(1-s)!· (1+R)/(1-R)!        (24)

where

    s=-Vs/V0

The constitution above gives almost the same benefits as mentioned inthe 4th embodiment.

In passing, in the 6th embodiment the opening echo level V0 is found byperforming a pre-measurement, but the pre-measurement can be omittedwhen diagnosing if the opening echo level V0 is found at the factorystage and loaded into non-volatile memory such as the ROM, etc.

This invention has been discussed in detail above by using embodiments,but the concrete constitution is not restricted to these embodiments,and any modifications in design that are not beyond the scope of theessence of this invention are also included in this invention. Forexample, ultrasonic oscillators constituting the transducer are notrestricted to thick oscillator types: flexible oscillator types are alsopossible. Similarly, the central frequency is not restricted to 2.5 MHz.And since the acoustic impedance of soft tissue Ma is close to acousticimpedance of water, the acoustic impedance of water can be used insteadof the acoustic impedance of soft tissue Ma in applying Equation (1)

INDUSTRIAL APPLICABILITY

The osteoporosis diagnosing apparatus and method of this invention issuitable for institutions such as hospitals and health centres; inaddition to being small and lightweight, the apparatus is easy tooperate, and moreover there is no danger of exposure to radiation, sothat it is very much preferable for use as equipment for healthmanagement in old peoples homes.

What is claimed is:
 1. An osteoporosis diagnosing apparatuscomprising:an ultrasonic transducer having a transducer surface forsubmitting and receiving ultrasonic impulses, said transducer surfaceadapted to be set on a skin of an examinee and repeatedly radiateultrasonic impulses from the transducer surface toward a surface of abone beneath the skin and receive at the transducer surface echos of theradiated ultrasonic impulses reflected at the surface of the bone whilea direction of the transducer surface is changed in various directionsincluding a direction perpendicular to the surface of the bone; an echolevel detector which detects echo levels of said echos; a maximum echoextraction unit which extracts a maximum echo level from the echo levelsdetected by said echo level detector; and a decision unit whichdetermines that the bone is osteoporosis when a value of said maximumecho level extracted by said maximum echo extraction unit is lower thana predetermined fixed value.
 2. An osteoporosis diagnosing apparatusaccording to claim 1, further comprising:an output unit which outputs aresult determined by said decision unit.
 3. An osteoporosis diagnosingapparatus comprising:an ultrasonic transducer having a transducersurface for emitting and receiving ultrasonic impulses, said transducersurface adapted to be set on a skin of an examinee and repeatedlyradiate ultrasonic impulses from the transducer surface toward a surfaceof a bone beneath the skin and receive at the transducer surface echosof the radiated ultrasonic impulses reflected at the surface of the bonewhile a direction of the transducer surface is changed in variousdirections including a direction perpendicular to the surface of thebone; an echo level detector which detects echo levels of said echos; amaximum echo extraction unit which extracts a maximum echo level fromthe echo levels detected by said echo level detector; a reflectioncoefficient calculator which calculates an ultrasonic reflectioncoefficient of the bone relative to soft tissue around the bone on thebasis of said maximum echo level; and a decision unit which determineswhether the bone is osteoporosis or not on the basis of the ultrasonicreflection coefficient calculated by said reflection coefficientcalculator.
 4. An osteoporosis diagnosing apparatus according to claim3, further comprising:a timing unit which determines an echo arrivaltime from a timing at which said ultrasonic transducer radiates theultrasonic impulse to a timing at which an echo of an ultrasonic impulseis received at said transducer surface, said reflection coefficientcalculator calculating the ultrasonic reflection coefficient on thebasis of the maximum echo level extracted by said maximum echoextraction unit and the echo arrival time determined by said timingunit.
 5. An osteoporosis diagnosing apparatus according to claim 4,wherein said reflection coefficient calculator calculates an attenuationdegree of the ultrasonic impulse during a round trip in the soft tissuebased on said echo arrival time when the maximum echo level is extractedby said maximum echo extraction unit, and further calculates an acousticimpedance of the bone of the examinee based on said attenuation degreeand said maximum echo level.
 6. An osteoporosis diagnosing apparatusaccording to claims 3, 4 or 5, wherein said decision unit determinesthat the bone is osteoporosis when a value of the ultrasonic reflectioncoefficient calculated by said reflection coefficient calculator issmaller than a predetermined reference value.
 7. An osteoporosisdiagnosing apparatus according to claim 3, further comprising:an outputunit which outputs a result determined by said decision unit.
 8. Anosteoporosis diagnosing apparatus comprising:an ultrasonic transducerhaving a transducer surface for emitting and receiving ultrasonicimpulses, said transducer surface adapted to be set on a skin of anexaminee and repeatedly radiate ultrasonic impulses from the transducersurface toward a surface of a bone beneath the skin and receive at thetransducer surface echos of the radiated ultrasonic impulses reflectedat the surface of the bone while a direction of the transducer surfaceis changed in various directions including a direction perpendicular tothe surface of the bone; an echo level detector which detects echolevels of said echos; a maximum echo extraction unit which extracts amaximum echo level from the echo levels detected by said echo leveldetector; an acoustic impedance calculator which calculates an acousticimpedance of the bone based on said maximum echo level extracted by saidmaximum echo extraction unit; and a decision unit which determineswhether the bone is osteoporosis or not on the basis of the acousticimpedance calculated by said acoustic impedance calculator.
 9. Anosteoporosis diagnosing apparatus according to claim 8, furthercomprising:a timing unit which determines an echo arrival time from atiming at which said ultrasonic transducer radiates the ultrasonicimpulse to a timing at which an echo of an ultrasonic impulse isreceived at said transducer surface, said acoustic impedance calculatorcalculating said acoustic impedance based on said maximum echo levelextracted by said maximum echo extraction unit and said echo arrivaltime determined by said timing unit.
 10. An osteoporosis diagnosingapparatus according to claim 9, wherein said acoustic impedancecalculator calculates an attenuation degree of the ultrasonic impulseduring a round trip in the soft tissue based on the echo arrival timewhen the maximum echo level is extracted by said maximum echo extractionunit, and further calculates the acoustic impedance of the bone of theexaminee based on said attenuation degree and said maximum echo level.11. An osteoporosis diagnosing apparatus according to claim 8, whereinsaid acoustic impedance calculator calculates an ultrasonic reflectioncoefficient of the bone relative to soft tissue around the bone based onsaid maximum echo level, and further calculates the acoustic impedanceof the bone based on said ultrasonic reflection coefficient.
 12. Anosteoporosis diagnosing apparatus according to claims 8, 9, 10 or 11,wherein said decision unit determines that the bone is osteoporosis whensaid acoustic impedance calculated by said acoustic impedance calculatoris smaller than a predetermined impedance reference value.
 13. Anosteoporosis diagnosing apparatus according to claim 8, furthercomprising:an output unit which outputs a result determined by saiddecision unit.
 14. An osteoporosis diagnosing apparatus comprising:anultrasonic transducer having a transducer surface for emitting andreceiving ultrasonic impulses, said transducer surface adapted to be seton a skin of an examinee and repeatedly radiate ultrasonic impulses fromthe transducer surface toward a surface of a bone beneath the skin andreceive at the transducer surface echos of the radiated ultrasonicimpulses reflected at the surface of the bone while a direction of thetransducer surface is changed in various directions including adirection perpendicular to the surface of the bone; an analogue digitalconverter which converts receiving signals of the echos into digitalecho signals; a program memory which stores a processing program whichincludes a routine for reading said digital echo signals output fromsaid analog digital converter, a routine for detecting echo levels basedon the digital echo signals, and a routine for extracting a maximum echolevel from the detected echo levels; and a central processing unit whichdetermines that the bone is osteoporosis when a value of said maximumecho level extracted by executing said processing program is lower thana predetermined fixed value.
 15. An osteoporosis diagnosing apparatuscomprising:an ultrasonic transducer having a transducer surface foremitting and receiving ultrasonic impulses, said transducer surfaceadapted to be set on a skin of an examinee and repeatedly radiateultrasonic impulses from the transducer surface toward a surface of abone beneath the skin and receive at the transducer surface echos of theradiated ultrasonic impulses reflected at the surface of the bone whilea direction of the transducer surface is changed in various directionsincluding a direction perpendicular to the surface of the bone; ananalogue digital converter which converts receiving signals of the echosinto digital echo signals; a program memory which stores a processingprogram which includes a routine for reading said digital echo signalsoutput from said analog digital converter, a routine for detecting echolevels based on the digital echo signals, a routine for extracting amaximum echo level from the detected echo levels, and a routine forcalculating an ultrasonic reflection coefficient of the bone relative tosoft tissue around the bone on the basis of said maximum echo level; anda central processing unit which calculates said ultrasonic reflectioncoefficient by executing said processing program and determines whetherthe bone is osteoporosis or not based on said ultrasonic reflectioncoefficient.
 16. An osteoporosis diagnosing apparatus according to claim15, further comprising:a timing unit which measures an echo arrival timefrom a timing at which said ultrasonic transducer radiates theultrasonic impulse to a timing at which an echo of an ultrasonic impulseis received at said transducer surface, said processing programincluding a procedure which calculates the ultrasonic reflectioncoefficient based on the maximum echo level and said echo arrival time.17. An osteoporosis diagnosing apparatus according to claim 16, whereinsaid program memory further stores as part of said processing program aprocedure which calculates an attenuation degree of the ultrasonicimpulse during a round trip in the soft tissue based on said echoarrival time when the maximum echo level is received, and a procedurewhich calculates the ultrasonic reflection coefficient based on saidattenuation degree and said maximum echo level.
 18. An osteoporosisdiagnosing apparatus according to claim 15, 16 or 17, wherein saidcentral processing unit determines that the bone is osteoporosis when avalue of said ultrasonic reflection coefficient is smaller than apredetermined reference value.
 19. An osteoporosis diagnosing apparatusaccording to claims 16 or 17, further comprising:an amplifying circuitsystem provided between said ultrasonic transducer and said analoguedigital transducer, wherein said central processing unit calculates theultrasonic reflection coefficient based on the following relationship,

    R=Ve/(P*Q*B*Vi*A(T)),

whereA(T): Attenuation degree of ultrasound wave during a round trip inthe soft tissue, T: Echo arrival time, P: Sound pressure of theultrasonic impulse output from the transducer surface in the directionperpendicular to the surface of the bone when a unit electrical signalis applied to the transducer, Q: Amplitude of the receiving signals whenan echo vertically incidents at the transducer surface, B: Total degreeof amplification of the amplifying circuit system, Vi: Amplitude of anelectrical signal applied to the ultrasonic transducer, and Ve: Maximumbone echo level.
 20. An osteoporosis diagnosing apparatus according toclaim 14, wherein said analogue digital converter comprises a rapidaccess sampling memory which temporarily stores said digital echosignals digitalized in a certain sampling period.
 21. An osteoporosisdiagnosing apparatus comprising:an ultrasonic transducer having atransducer surface for emitting and receiving ultrasonic impulses, saidtransducer surface adapted to be set on a skin of an examinee andrepeatedly radiate ultrasonic impulses from the transducer surfacetoward a surface of a bone beneath the skin and receive at thetransducer surface echos of the radiated ultrasonic impulses reflectedat the surface of the bone while a direction of the transducer surfaceis changed in various directions including a direction perpendicular tothe surface of the bone; an analogue digital converter which convertsreceiving signals of the echos into digital echo signals; a programmemory which stores a processing program which includes a routine forreading said digital echo signals output from said analog digitalconverter, a routine for detecting echo levels based on the digital echosignals, a routine for extracting a maximum echo level from the detectedecho levels, and a routine for calculating an acoustic impedance of thebone based on said extracted maximum echo level; and a centralprocessing unit which calculates the acoustic impedance by executingsaid processing program and determines whether the bone is osteoporosisbased on said acoustic impedance of the bone.
 22. An osteoporosisdiagnosing apparatus according to claim 21, further comprising:a timingunit which measures an echo arrival time from a timing at which saidultrasonic transducer radiates the ultrasonic impulse to a timing atwhich an echo of an ultrasonic impulse is received at said transducersurface, said processing program including a procedure which calculatesan ultrasonic reflection coefficient of said bone relative to softtissue around the bone based on the maximum echo level and said echoarrival time.
 23. An osteoporosis diagnosing apparatus according toclaim 21, wherein said program memory further stores as part of saidprocessing program a procedure which calculates an attenuation degree ofthe ultrasonic impulse during a round trip in the soft tissue based onsaid echo arrival time when the maximum echo level is received, and aprocedure which calculates the ultrasonic reflection coefficient basedon said attenuation degree and said maximum echo level.
 24. Anosteoporosis diagnosing apparatus according to claim 21, wherein saidprogram memory further stores as part of said processing program aprocedure which calculates said ultrasonic reflection coefficient basedon said maximum echo level, and a procedure which calculates theacoustic impedance based on said ultrasonic reflection coefficient. 25.An osteoporosis diagnosing apparatus according to claims 21, 22, 23 or24, wherein said processing unit determines that the bone isosteoporosis when said acoustic impedance is smaller than apredetermined impedance reference value.
 26. An osteoporosis diagnosingapparatus according to claims 15 or 24, wherein said central processingunit calculates the ultrasonic reflection coefficient based on thefollowing relationship,R=Ve/V0, whereVe: Maximum echo level, and V0:Total echo level of an ultrasonic impulse from the ultrasonictransducer.
 27. An osteoporosis diagnosing apparatus according to claims15 or 24, further comprising:an amplifying circuit system providedbetween said ultrasonic transducer and said analogue digital transducer,wherein said central processing unit calculates the ultrasonicreflection coefficient based on the following relationship,

    R=Ve/P*Q*B*Vi,

whereP: Sound pressure of the ultrasonic impulse output from thetransducer surface in the direction perpendicular to the surface of thebone when a unit electrical signal is applied to the transducer, Q:Amplitude of the receiving signals when an echo vertically incidents atthe transducer surface, B: Total degree of amplification of theamplifying circuit system, Vi: Amplitude of an electrical signal appliedto the ultrasonic transducer, and Ve: Maximum echo level.
 28. Anosteoporosis diagnosing apparatus according to claims 29, 22 or 23,wherein said central processing unit calculates the acoustic impedanceof the bone based on the following relationship,

    Zb=Za(Ve/V0+1)/(1-Ve/V0),

whereZb: Acoustic impedance of the bone, Za: Acoustic impedance of softtissue or water, Ve: Maximum echo level, and V0: Total echo level of anultrasonic impulse radiated from the ultrasonic transducer.
 29. Anosteoporosis diagnosing apparatus according to claims 21, 22, 23 or 24,wherein said central processing unit calculates the acoustic impedanceof the bone based on the following relationship,

    Zb=Za(R+1)/(1-R),

whereZa: Acoustic impedance of soft tissue or water, and R: Ultrasonicreflection coefficient of the bone relative to the soft tissue aroundthe bone.
 30. An osteoporosis diagnosing apparatus according to claim14, further comprising:a data memory which temporarily memorizes dataincluding said detected echo levels and said maximum echo level, whereinsaid data memory has an area which stores a currently detected echolevel and the maximum echo level, and said processing program includes aroutine for comparing the currently detected echo level with the maximumecho level and a routine for updating the maximum echo level with thecurrently detected echo level when the currently detected echo level isgreater than the maximum echo level.
 31. An osteoporosis diagnosingapparatus according to claim 14, further comprising:a data memory whichtemporarily memorizes data including said detected echo levels and saidmaximum echo level, wherein said data memory has an area which storesall of the echo levels and the maximum echo level detected during awhole detection period by said processing program, and said processingprogram includes a routine for extracting the maximum echo level fromthe echo levels stored in said data memory.
 32. An osteoporosisdiagnosing apparatus according to claim 14, further comprising:a datamemory which temporarily memorizes data including said detected echolevels and said maximum echo level, said data memory having an areawhich stores a currently detected echo level and the maximum echo level;and a level display which simultaneously displays the currently detectedecho level and the maximum echo level.
 33. An osteoporosis diagnosingapparatus comprising:an ultrasonic transducer including a transducersurface for emitting and receiving ultrasonic impulses and an ultrasonicwave retarding spacer attached to the transducer surface, saidultrasonic transducer adapted to be set on a skin of an examinee at theultrasonic wave retarding spacer and repeatedly radiate ultrasonicimpulses from the transducer surface toward a surface of a bone beneaththe skin and receive at the transducer surface a first echo reflected ata surface of the skin and a second echo reflected at the surface of thebone while a direction of the transducer surface is changed in variousdirections including a direction perpendicular to the surface of thebone; an analogue digital converter which converts receiving signals ofthe first and second echos into first and second digital echo signals; aprogram memory which stores a processing program including a routinewhich measures an echo arrival time difference between a timing at whichthe first echo is received at the transducer surface and a timing atwhich the second echo is received at the transducer surface, a routinewhich detects first and second echo levels from the first and seconddigital echo signals, a routine which extracts a maximum echo level fromthe detected second echo levels, a routine which calculates anultrasonic reflection coefficient of the bone relative to soft tissuearound the bone based on the maximum echo level and the echo arrivaltime difference; and a central processing unit which calculates anultrasonic reflection coefficient by executing said processing program,and determines whether the bone is osteoporosis based on the ultrasonicreflection coefficient.
 34. An osteoporosis diagnosing apparatusaccording to claim 33, wherein said central processing unit calculatesthe ultrasonic reflection coefficient based on the followingrelationship,

    R=((Za+Zc)*(Za-Zc)*Ve)/(4Za*Zc*A(T)*Vs),

whereZc: Acoustic impedance of the ultrasonic wave retarding spacer, Za:Acoustic impedance of soft tissue, Ve: Maximum echo level, Vs: Firstecho level when maximum echo level is received, T: Echo arrival timedifference when maximum echo level is received, and A(T): Attenuationdegree of ultrasound wave when maximum echo level is received.
 35. Anosteoporosis diagnosing apparatus comprising:an ultrasonic transducerincluding a transducer surface for emitting and receiving ultrasonicimpulses and an ultrasonic wave retarding spacer attached to thetransducer surface, said ultrasonic transducer adapted to be set on askin of an examinee at the ultrasonic wave retarding spacer andrepeatedly radiate ultrasonic impulses from the transducer surfacetoward a surface of a bone beneath the skin and receive at thetransducer surface a first echo reflected at a surface of the skin and asecond echo reflected at the surface of the bone while a direction ofthe transducer surface is changed in various directions including adirection perpendicular to the surface of the bone; an analogue digitalconverter which converts receiving signals of the first and second echosinto first and second digital echo signals; a program memory whichstores a processing program including a routine which measures an echoarrival time difference between a timing at which the first echo isreceived at the transducer surface and a timing at which the second echois received at the transducer surface, a routine which detects first andsecond echo levels from the first and second digital echo signals, aroutine which extracts a maximum echo level from the detected secondecho levels, a routine which calculates an acoustic impedance of thebone based on the maximum echo level and the echo arrival timedifference; and a central processing unit which calculates the acousticimpedance by executing said processing program, and determines whetherthe bone is osteoporosis based on the acoustic impedance.
 36. Anosteoporosis diagnosing apparatus according to claim 35, wherein saidprogram memory further stores as part of said processing program aroutine which calculates an ultrasonic reflection coefficient of thebone relative to soft tissue around the bone based on said maximum echolevel, said first echo level and said echo arrival time difference, anda routine which calculates said acoustic impedance of the bone based onsaid ultrasonic reflection coefficient.
 37. An osteoporosis diagnosingapparatus according to claim 36, wherein said central processing unitcalculates the acoustic impedance of the bone based on the followingrelationship,

    Zb=Zc*((1+s)/(1-s))*((1+R)/(1-R)),

wheres=-Vs/V0, V0: Echo level returned from an end surface of theultrasonic wave retarding spacer when an ultrasonic impulse is radiatedtoward air, R: Ultrasonic reflection coefficient of the bone relative tothe soft tissue around the bone, and Zc: Acoustic impedance of theultrasonic wave retarding spacer.
 38. An osteoporosis diagnosingapparatus comprising:an ultrasonic transducer including a transducersurface for emitting and receiving ultrasonic impulses and an ultrasonicwave retarding spacer attached to the transducer surface, saidultrasonic transducer adapted to be set on a skin of an examinee at theultrasonic wave retarding spacer and repeatedly radiate ultrasonicimpulses from the transducer surface toward a surface of a bone beneaththe skin and receive at the transducer surface a first echo reflected ata surface of the skin and a second echo reflected at the surface of thebone while a direction of the transducer surface is changed in variousdirections including a direction perpendicular to the surface of thebone; an analogue digital converter which converts receiving signals ofthe first and second echos into first and second digital echo signals; apremeasurement program having a routine which determines an open timeecho level when an ultrasonic impulse is radiated towards air and whenan open time echo from an end of said ultrasonic wave retarding spaceris received by said ultrasonic oscillator; a main measurement programhaving a routine which measures an echo arrival time difference betweena timing at which the first echo is received at the transducer surfaceand a timing at which the second echo is received at the transducersurface, a routine which detects first and second echo levels from thefirst and second digital echo signals, a routine which extracts amaximum echo level from the detected second echo levels, a routine whichcalculates an ultrasonic reflection coefficient of the bone relative tosoft tissue around the bone based on the maximum echo level, the firstecho level, and the echo arrival time difference; a program memory whichstores said premeasurement program and said main measurement program;and a central processing unit which calculates an ultrasonic reflectioncoefficient by executing said main measurement program, and determineswhether the bone is osteoporosis based on the ultrasonic reflectioncoefficient.
 39. An osteoporosis diagnosing apparatus according to claim38, wherein said central processing unit calculates the ultrasonicreflection coefficient based on the following relationship,

    R=h/((1+s)*(1-s)*A(T)),

whereh=-Ve/V0, s=-Vs/V0, Ve: Maximum echo level, Vs: First echo levelwhen maximum bone echo level is received, T: Bone echo arrival timedifference when maximum bone echo level is received, A(T): Attenuationdegree of ultrasound wave when maximum bone echo level is received, andV0: Open time echo level.
 40. An osteoporosis diagnosing apparatuscomprising:an ultrasonic transducer including a transducer surface foremitting and receiving ultrasonic impulses and an ultrasonic waveretarding spacer attached to the transducer surface, said ultrasonictransducer adapted to be set on a skin of an examinee at the ultrasonicwave retarding spacer and repeatedly radiate ultrasonic impulses fromthe transducer surface toward a surface of a bone beneath the skin andreceive at the transducer surface a first echo reflected at a surface ofthe skin and a second echo reflected at the surface of the bone while adirection of the transducer surface is changed in various directionsincluding a direction perpendicular to the surface of the bone; ananalogue digital converter which converts receiving signals of the firstand second echos into first and second digital echo signals; a programmemory which stores a main measurement program having a routine whichmeasures an echo arrival time difference between a timing at which thefirst echo is received at the transducer surface and a timing at whichthe second echo is received at the transducer surface, a routine whichdetects first and second echo levels from the first and second digitalecho signals, a routine which extracts a maximum echo level from thedetected second echo levels, a routine which calculates an ultrasonicreflection coefficient of the bone relative to soft tissue around thebone based on the maximum echo level, the first echo level, and the echoarrival time difference, and a routine which calculates the acousticimpedance of the bone based on said ultrasonic reflection coefficient;and a central processing unit which calculates said acoustic impedanceby executing said main measurement program, and determines whether thebone is osteoporosis based on said acoustic impedance.
 41. Anosteoporosis diagnosing apparatus according to claim 40, wherein saidcentral processing unit calculates the acoustic impedance of the bonebased on the following relationship,

    Zb=Zc*((1+s)/(1-s))*((1+R)/(1-R)),

wheres=-VS/V0, V0: Open echo level, R: Ultrasonic reflection coefficientof the bone relative to the soft tissue around the bone, and Zc:Acoustic impedance of the ultrasonic wave retarding spacer.
 42. Anosteoporosis diagnosing method comprising the steps of:setting anultrasonic transducer on a skin of an examinee; repeatedly radiatingultrasonic impulses from a transducer surface of said ultrasonictransducer toward a surface of a bone beneath the skin while a directionof the transducer surface is changed in various directions including adirection perpendicular to the surface of the bone; receiving at thetransducer surface echos of the radiated ultrasonic impulses reflectedthe surface of the bone; measuring echo levels of said echos;determining a maximum echo level from the measured echo levels;estimating a bone density or bone elastic modulus based on said maximumecho level; calculating an ultrasonic reflection coefficient of the bonerelative to soft tissue around the bone on the basis of said maximumecho level; and determining whether the bone is osteoporosis on thebasis of said ultrasonic reflection coefficient.
 43. An osteoporosisdiagnosing method comprising the steps of:setting an ultrasonictransducer on a skin of an examinee; repeatedly radiating ultrasonicimpulses from a transducer surface of said ultrasonic transducer towarda surface of a bone beneath the skin while a direction of the transducersurface is changed in various directions including a directionperpendicular to the surface of the bone; receiving at the transducersurface echos of the radiated ultrasonic impulses reflected the surfaceof the bone; measuring echo levels of said echos; determining a maximumecho level from the measured echo levels; estimating a bone density orbone elastic modulus based on said maximum echo level; calculating anacoustic impedance of the bone on the basis of said maximum echo level;and determining whether the bone is osteoporosis on the basis of saidacoustic impedance.
 44. An osteoporosis diagnosing method according toclaim 43, further comprising:a step of calculating an ultrasonicreflection coefficient of the bone relative to soft tissue around thebone on the basis of said maximum echo level, wherein the step ofcalculating said acoustic impedance is performed on the basis of saidultrasonic reflection coefficient.